To secure brightness evenness on a display surface of a liquid crystal display apparatus, a backlight built in the liquid crystal display apparatus is strongly required to have brightness evenness for the entire surface of a light emitting surface (active area) that shines a liquid crystal panel. Because of this, in a backlight, conventionally, brightness evenness required for an active area is secured by complicatedly combining a plurality of sheets.
In a method for using several kinds of sheets, because a structure in accordance with use is possible, the degree of freedom of the structure is high; however, because of a large number of sheets and kinds of them, there are problems of complicated designing for securing evenness, much assembly manpower and high cost. To improve these, several methods are proposed as methods that reduce the number of sheets.
For example, a backlight of a reversed-prism type in which uses a prism sheet on one surface of which a prism train is formed with the prism sheet faced with a light-guide plate side is disclosed in a patent document 1 and a patent document 2. Besides, a backlight that has a structure in which a micro-prism array sheet and a light guide plate are unitarily formed with each other is disclosed in a patent document 3 and a patent document 4.    [patent document 1]: JP-A-1994-18879    [patent document 2]: JP-A-2003-302508    [patent document 3]: JP-A-2002-15611    [patent document 4]: JP-A-2002-42528